Using Orthographic Projection and ArcGIS to Constrain the Kinematics of Folding in the Central Range Fault Zone, Trinidad

The Central Range fault zone marks the boundary between the Caribbean and South American plates in Trinidad. Based on GPS measurements, this boundary is thought to be dextral transpressional in nature. Finding the strike and dip of bedding on the limbs of folds near the Central Range fault make it is possible to constrain past tectonic conditions of the area. This tropical, low relief area, however, lacks sufficient outcrop to accurately measure the fold limb orientation. Therefore an alternate approach is needed to gather information about the folds in order to gather the data necessary for this study. Both a geologic map and a 30 m digital elevation model (DEM) are available for Trinidad. Using ArcGIS these two maps were superimposed and georeferenced. This allowed the contacts of the folds on the geologic map to be located and recorded using UTM measurements and elevation data from the DEM. A script written in MATLAB converted these XYZ data to strike and dip measurements using standard orthographic projection techniques (i.e. the three point problem). The cylindrical best fit to this population of bedding orientations was used to calculate the orientation of the fold axis. Comparison of the average limb dip to fold axis orientation relative to the Central Range fault allows for the angle of oblique convergence to be calculated. This angle describes relative plate motion between the two plates. These data suggest that the relative amount of convergent plate motion increases symmetrically away from the Central Range fault. Conversely, the transcurrent motion systematically increases closer to the fault. Partitioning of the strike-slip component of deformation towards the center of a shear zone follows the pattern expected for a transpressional fault zone. This supports the hypothesis that transpressional deformation has been long lived in the Central Range fault zone.